Evaluation of Active Drag in Swimming Using the Surface and Submerged Hydrodynamic Body Technique 711

Abstract

A recent technique is employed to assess active drag in elite U.S. swimmers. This technique, described by Kolmogorov and Duplishcheva(1992), requires a swimmer to perform two separate maximal 50 meter sprints while untethered and tethered to a hydrodynamic drag device of known drag. Comparing the mean velocities over 30 meters of free swimming to tethered swimming allows for the computation of active drag (Fad) during the untethered sprint. This device is a metal cylinder filled with water and supported by a carrying board made of penoplast. Video analysis reveals significant deviations in pitch, roll, yaw, and lateral positioning behind the swimmer even at the derived non-turbulent towing distance of at least 3.5 to 4.5 times the swimmer's body length. The device also imparts a strenuous load on the less powerful swimmers, possibly changing the mechanics of their stroke. These concerns lead to design of a new hydrodynamic drag device. This device is an elongated funnel which maintains a stable submerged position, and imparts enough load to vary velocities yet keep changes in stroke mechanics to a minimum. In this study all athletes, 9 males and 9 females ranging from division II to division I abilities, perform trials of maximal tethered and untethered sprints of two strokes with both the new and old devices. The mean active drag values obtained using the new device are 40% - 50% lower than the old device, depending on stroke. The deviation is due in part to the absence of turbulence during calibration and are accounted for with a correction factor. The remaining magnitude variation is attributed to the increased accuracy, stability and predictable fluid dynamic performance of the new device.